Gold is generally alloyed with other metals for use in jewelry and in dentistry. Such alloys require a relatively low melting point and must form a generally fluid melt with a low surface tension to permit conformance to intricate molds. When used in jewelry, gold alloys must preserve the look of gold and should be capable of being readily worked and polished. In the dental field as in the jewelry field, corrosion and tarnishing are a concern and gold alloys should not easily tarnish and corrode.
In jewelry application, color is a particularly important feature. Gold, Copper and Silver are generally used to adjust color with copper always used with the gold color jewelry alloys. In dentistry application, gold alloys are used for restorations and bridges, inlays and partial dentures. These applications must be castable and in fact replaced wrought wire in many of these appliances. In attempts of the prior art to develop a gold alloy possessing the true color of gold while maintaining its capabilities of being readily workable and polished, various non-precious metals and gold have been tried. For example, the present applicants U.S. Pat. No. 4,350,527 is directed to a gold colored alloy having 0 to 10 percent gold content with 7 to 20 percent copper, 15 to 20 percent indium and 5 to 15 percent palladium.
A number of U.S. Patents describe gold alloys for use in jewelry and dentistry, but all contain copper. U.S. Pat. No. 1,987,451 contains 25 to 65 percent gold, 2 to 25 percent palladium, 10 to 33 percent silver, 10 to 25 percent copper and 0.5 to 5 percent indium. U.S. Pat. No. 4,264,359 contains 25 percent gold, 12 to 13 percent palladium, 10 to 12 percent silver, 9 to 10 percent zinc, 0.045 to 0.65 percent boron, and the balance consisting of copper. U.S. Pat. No. 4,370,164 contains 4 to 10 percent gold, 54 to 61 percent silver, 14 to 19 percent copper, 4 to 7 percent palladium, 9 to 14 percent indium and 1 to 3 percent zinc. All of these patents include a substantial percentage of copper by weight to achieve the gold colored alloy. U.S. Pat. No. 4,038,074 discloses a nickel-chromium based alloy containing 63 to 75 nickel, 17 to 22 percent chromium, 2.5 to 5 percent molybdenum, 1 to 5 percent cobalt, 2 to 3 percent boron, 0 to 1 percent iron, and 0 to 5 percent copper, with the preferred embodiment having 0 percent copper. However, this patent is for a metal alloy which is not gold colored.